There is a connection problem with the database you can use the Tnsping service name at the command line to check the cause of the error.
Common errors are:
Ora-12535:tns: Operation timeout
Turn off the firewall first, which is the most common connection error reason.
If still not, check the Tnsnames.ora file configuration, mainly whether the host name is correct
# TNSNAMES.ORA Network Configuration File: E:\oracle\ora92\network\admin\tnsnames.ora
# Generated by Oracle configuration tools.
ORCL.DBSE.LAMOST =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.1)(PORT = 1521))
)
(CONNECT_DATA =
(SID = orcl)
(SERVER = DEDICATED)
)
)
ORCL =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.1)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = orcl.dbse.lamost)
)
)
Ora-12541:tns: No listeners
Execute the LSNRCTL start listener at the command line.